Method of manufacturing a storage cathode and cathode manufactured by said method

ABSTRACT

A method of manufacturing a storage cathode comprising the steps of forming a first layer of electron emissive material in a holder, said layer comprising a loose mixture of coarse and fine granulated particles of electron emissive material, depositing on said first layer a second layer consisting essentially of loose tungsten particles and compressing said layer in the holder at the sintering temperature below the fusion temperature of the electron emissive material to sinter the second layer and form a unitary body of the layer in the holder.

United States Patent Van Stratum et al.

[ 1 Oct. 15, 1974 METHOD OF MANUFACTURING A STORAGE CATHODE AND CATl-lODE MANUFACTURED BY SAID METHOD Inventors: Antonius Johannes Alberta Van Stratum; Franciscus Johannes Verest; Wilheim Ernst Paul Parchen, all of Emmasingel, Eindhoven, Netherlands U.S. Philips Corporation, New York, NY.

Filed: Nov. 30, 1972 Appl. No.: 310,864

Related U.S. Application Data Continuation of Ser. No. 88,643, Nov. 12, 1970, abandoned.

Assignee:

U.S. (:1. 313/346 DC, 29/2517, 313/337, 313/346 R Int. Cl. ......H01j 1/14, HOlj 19/02, HOlj 19/06 Field of Search 29/251, 25.11, 25.13, 29/2514, 25.17, 25.18; 313/346 R, 346 DC, 337

References Cited UNITED STATES PATENTS 12/1952 Jansen et al. 29/2517 X 2,722,626 11/1955 Coppola et al. 29/25.]7 X 3,113,236 12/1963 Lcmmens ct a1 313/346 DC 3,148,056 9/1964 Brodie et al. 29/25.l4 X 3,155,864 11/1964 Coppola 313/346 R 3,497,757 2/1970 Zalm et a1 313/346 R Primary Examiner-Roy Lake Assistant Examiner-.1. W. Davie Attorney, Agent, or FirmFrank R. Trifari [57] ABSTRACT 8 Claims, 2 Drawing Figures PATENTEDDBHSW 3.842309 INVEN'IY'OI-ZS ANTONIUS J.A'. VAN STRATUM FRANCISCUS J-. VEREST- WILHELM E.P. PARCHEN AGENT v METHOD OF MANUFACTURING A STORAGE CATHODE AND CATHODE MANUFACTURED BY SAID METHOD This is a continuation, of application Ser. No. 88,643, filed Nov. 12, 1970, now abandoned.

The invention relates to a method of manufacturing a storage cathode, in particular a cathode in which several layers compressed from snail particles and sintered, are pressed one on the other in a holder. The invention furthermore relates to a cathode manufactured according to this method.

A storage cathode is known from German Patent specification No. 1,012,382 in which active constituents consisting of fine powder are compressed to form a pellet which is provided in a holder after which a quantity of annealed tungsten powder is poured on said pellet, compressed and weakly sintered. Shrinkage of the compressed material does not occur as a result of this. The use of powdered materials, however, suffers from the drawback that the danger of jamming of the dies by adhering powder exists. Furthermore, in the case of too strong a compression, too fine pores are formed as a result of which the barium migration occurs too slowly so that it is difficult to obtain a constant porosity for the various cathodes, since the fineness of the pores is considerably dependent upon the pressure of compression.

These drawbacks can be entirely avoided in a method of manufacturing a storage cathode in which several sintered layers consisting of small particles are compressed one on the other in a holder, if, according to the invention the raw materials for at least two layers to be provided one on the other, are poured in grain form one over the other and are together compressed in the holder and then sintered.

By using raw materials in grain form, porous layers are obtained the density of which is reproducible in that the dimensions of the pores are little dependent upon the pressure of compression and in addition a lium, however, is undesirable as a result of the accumulatively poisonous character of said element.

In order that the invention may be readily carried into effect, one embodiment thereof will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which FIG. 1 shows an arrangement for compressing the layers in a cap, while FIG. 2 shows a cathode manufactured according to the invention.

In FIG. 1, reference numeral 1 denotes a molybdenum cap which is placed in a lower matrix 2.

A ring 3 is placed on the lower matrix 2, after which a layer consisting of a mixture of tungsten grains and barium-calcium-aluminate in grain form is poured in the cap 1. The grain size is from 36 to 135g. The granulate is then still pourable.

. A layer 5 consisting of tungsten grains is then poured on the layer 4. A die 6 is then forced into the cavity so that the layers 4 and 5 are compressed at a pressure of 10,000 kg/sc.cm. The quantities of material of the layers 4 and 5 are chosen to be so that after compression the molybdenum cap 1 is just filled. lf desirable, the

layers are then covered by an osmium layer 11 and sintered at l,550'C, i.e., just below the melting temperature of l,600 C of the aluminate. The cap 1 is then between the grains, the active substances can be better released. Moreover, the comparatively coarse grains prevent the dies from jamming and getting clogged.

The uppermost layer after compression but prior to sintering can be first covered with an osmium layer. Another advantage of the use of granular raw materials is that each grain may consist of a composition of various components. So grains, consisting, for example, of a barium compound with a strong reduction agent, which grains hence rapidly release barium, may be mixed with grains consisting of a barium compound from which barium is released slowly. Initially the cathode supplies proportionally much barium which is desirable for making gases which initially are still present in the tube and are being released harmless, while the cathode, as a result of the presence of the grains which release barium slowly, has a long lifetime.

The pressure of compression must be so high as to give the layer consisting of tungsten particles a density of 75 percent. Such a layer has been found not to shrink during sintering, so that it does not work loose in the holder.

welded to a sleeve 8 (FIG; 2), suspension strips 7 being laid between the cap land the sleeve 8 and being simultaneously welded. The filament 9 with insulating material 10 is then provided in the sleeve 8 and the cathode can be incorporated in a tube.

The grains for the layer 4 are obtained by mixing, for example, from 20 to percent by weight of fine tungsten powder with powdered coprecipitated barium carbonate, calcium carbonate and aluminium oxide in the molecular ratio 5, 3, 2. The mixture is compressed to a block, sintered and ground, after which the grains having dimensions between 36 and p. are sieved out.

Furthermore, grains are manufactured which consist of the said mixture of tungsten with barium-calciumaluminium compound to which, however, for example, 3 percent by weight of a reducing agent, for example, carbon, thorium, titanium or zirconium, has been added. These grains give off barium in a comparatively short time.

The two above-mentioned types of grains which contain aluminates, are mixed, for example, in the ratio 1 3, and are poured in the cap 1 as a layer 4. Afterwards, the grains which contain the reduction agent will rapidly give off barium as aresult of which residual gases and gases which are released in the tube can be rendered harmless. The remaining grains which contain only tungsten and barium-calcium aluminate release barium much more slowly and determine the lifetime of the cathode.

If the layer 5 is compressed to a density of 75 percent it is found substantially not to shrink during sintering and during operation, so that it remains tightly kept in the cap 1. By means of the said method, cathodes as shown in FIG. 2 can be manufactured in a cheap manner and they may also be applied in tubes in which comparatively much residual gases and releasing gases occur, for example, cathode ray tubes, travelling wave tubes, magnetrons and image intensifier tubes.

Although only one example has been described, the

invention may also be applied to differently shaped cathodes, of which, however, the manufacture will in general become more complicated and hence more expensive.

What is claimed is:

l. A method of manufacturing a storage cathode comprising the steps of a. providing a holder defining a cavity portion;

b. forming in said cavity portion a first layer comprising a loose mixture of coarse and fine granulated particles containing electron emissive material, only one of said coarse and fine granulated particles comprising a reducing agent;

c. depositing on said first layer a second layer consisting essentiallyv of loose particles of refractory metal; v

d. compressing at least said first and second layers simultaneously in said holder, and, then,

e. heating the compressed said layers at a temperature below the fusion temperature of said electron emissive material, thereby to sinter said layers and form a unitary body of porous said first and second layers in said holder.

2. A method as recited in claim 1, wherein said first layer comprises coarse particles of tungsten, barium compounds and a reducing agent selected from the group consisting of carbon, thorium, titanium, and zirconium.

3. A method of manufacturing as recited in claim 1, further comprising coating said compressed layers with an osmium layer prior to the sintering step.

4. A cathode produced according to claim 1, comprising said porous first layer consisting essentially of tungsten, barium compounds, and a reducing agent selected from the group consisting of carbon, thorium, titanium, and zirconium, said porous second layer consists essentially of tungsten, and a third layer consisting essentially of osmium disposed on said second layer.

5. A cathode as defined in claim 4, comprising said holder containing said first and second layers, a sleeve member on which said holder is disposed, and suspension members between said sleeve member and said holder, said holder, sleeve member, and suspension members being welded together.

6'. A method as in claim 1, wherein said fine particles comprise said reducing agent.

7. A method as in claim 1, wherein said coarse particles have a size in the range of about 36 to 135 microns.

8. A method as in claim-1, wherein said coarse and fine particles are present in the ratio of about 3:1, respectively. 

1. A method of manufacturing a storage cathode comprising the steps of a. providing a holder defining a cavity portion; b. forming in said cavity portion a first layer comprising a loose mixture of coarse and fine granulated particles containing electron emissive material, only one of said coarse and fine granulated particles comprising a reducing agent; c. depositing on said first layer a second layer consisting essentially of loose particles of refractory metal; d. compressing at least said first and second layers simultaneously in said holder, and, then, e. heating the compressed said layers at a temperature below the fusion temperature of said electron emissive material, thereby to sinter said layers and form a unitary body of porous said first and second layers in said holder.
 2. A method as recited in claim 1, wherein said first layer comprises coarse particles of tungsten, barium compounds and a reducing agent selected from the group consisting of carbon, thorium, titanium, and zirconium.
 3. A method of manufacturing as recited in claim 1, further comprising coating said compressed layers with an osmium layer prior to the sintering step.
 4. A cathode produced according to claim 1, comprising said porous first layer consisting essentially of tungsten, barium compounds, and a reducing agent selected from the group consisting of carbon, thorium, titanium, and zirconium, said porous second layer consists essentially of tungsten, and a third layer consisting essentially of osmium disposed on said second layer.
 5. A cathode as defined in claim 4, comprising said holder containing said first and second layers, a sleeve member on which said holder is disposed, and suspension members between said sleeve member and said holder, said holder, sleeve member, and suspension members being welded together.
 6. A method as in claim 1, wherein said fine particles comprise said reducing agent.
 7. A method as in claim 1, wherein said coarse particles have a size in the range of about 36 to 135 microns.
 8. A method as in claim 1, wherein said coarse and fine particles are present in the ratio of about 3:1, respectively. 